NAME

       RRDs - Access RRDtool as a shared module

SYNOPSIS

         use RRDs;
         RRDs::error
         RRDs::last ...
         RRDs::info ...
         RRDs::create ...
         RRDs::update ...
         RRDs::updatev ...
         RRDs::graph ...
         RRDs::fetch ...
         RRDs::tune ...
         RRDs::times(start, end)
         RRDs::dump ...
         RRDs::restore ...
         RRDs::flushcached ...
         RRDs::register_fetch_cb ...
         $RRDs::VERSION

DESCRIPTION

   Calling Sequence
       This module accesses RRDtool functionality directly from within Perl. The arguments to the
       functions listed in the SYNOPSIS are explained in the regular RRDtool documentation. The
       command line call

        rrdtool update mydemo.rrd --template in:out N:12:13

       gets turned into

        RRDs::update ("mydemo.rrd", "--template", "in:out", "N:12:13");

       Note that

        --template=in:out

       is also valid.

       The RRDs::times function takes two parameters:  a "start" and "end" time.  These should be
       specified in the AT-STYLE TIME SPECIFICATION format used by RRDtool.  See the rrdfetch
       documentation for a detailed explanation on how to specify time.

   Error Handling
       The RRD functions will not abort your program even when they can not make sense out of the
       arguments you fed them.

       The function RRDs::error should be called to get the error status after each function
       call. If RRDs::error does not return anything then the previous function has completed its
       task successfully.

        use RRDs;
        RRDs::update ("mydemo.rrd","N:12:13");
        my $ERR=RRDs::error;
        die "ERROR while updating mydemo.rrd: $ERR\n" if $ERR;

   Return Values
       The functions RRDs::last, RRDs::graph, RRDs::info, RRDs::fetch and RRDs::times return
       their findings.

       RRDs::last returns a single INTEGER representing the last update time.

        $lastupdate = RRDs::last ...

       RRDs::graph returns an ARRAY containing the x-size and y-size of the created image and a
       pointer to an array with the results of the PRINT arguments.

        ($result_arr,$xsize,$ysize) = RRDs::graph ...
        print "Imagesize: ${xsize}x${ysize}\n";
        print "Averages: ", (join ", ", @$averages);

       RRDs::info returns a pointer to a hash. The keys of the hash represent the property names
       of the RRD and the values of the hash are the values of the properties.

        $hash = RRDs::info "example.rrd";
        foreach my $key (keys %$hash){
          print "$key = $$hash{$key}\n";
        }

       RRDs::graphv takes the same parameters as RRDs::graph but it returns a pointer to hash.
       The hash returned contains meta information about the graph. Like its size as well as the
       position of the graph area on the image.  When calling with and empty filename than the
       contents of the graph will be returned in the hash as well (key 'image').

       RRDs::updatev also returns a pointer to hash. The keys of the hash are concatenated
       strings of a timestamp, RRA index, and data source name for each consolidated data point
       (CDP) written to disk as a result of the current update call. The hash values are CDP
       values.

       RRDs::fetch is the most complex of the pack regarding return values. There are 4 values.
       Two normal integers, a pointer to an array and a pointer to a array of pointers.

         my ($start,$step,$names,$data) = RRDs::fetch ...
         print "Start:       ", scalar localtime($start), " ($start)\n";
         print "Step size:   $step seconds\n";
         print "DS names:    ", join (", ", @$names)."\n";
         print "Data points: ", $#$data + 1, "\n";
         print "Data:\n";
         for my $line (@$data) {
           print "  ", scalar localtime($start), " ($start) ";
           $start += $step;
           for my $val (@$line) {
             printf "%12.1f ", $val;
           }
           print "\n";
         }

       RRDs::xport exposes the rrdxport functionality and returns data with the following
       structure:

         my ($start,$end,$step,$cols,$names,$data) = RRDs::xport ...

         # $start : timestamp
         # $end   : timestamp
         # $step  : seconds
         # $cols  : number of returned columns
         # $names : arrayref with the names of the columns
         # $data  : arrayref of arrayrefs with the data (first index is time, second is column)

       RRDs::times returns two integers which are the number of seconds since epoch (1970-01-01)
       for the supplied "start" and "end" arguments, respectively.

       See the examples directory for more ways to use this extension.

   Fetch Callback Function
       Normally when using graph, xport or fetch the data you see will come from an actual rrd
       file.  Some people who like the look of rrd charts, therefore export their data from a
       database and then load it into an rrd file just to be able to call rrdgraph on it. Using a
       custom callback, you can supply your own code for handling the data requests from graph,
       xport and fetch.

       Todo this, you have to first write a fetch function in perl, and then register this
       function using "RRDs::fetch_register_callback".

       Finally you can use the pseudo path name cb//[filename] to tell rrdtool to use your
       callback routine instead of the normal rrdtool fetch function to organize the data
       required.

       The callback function must look like this:

         sub fetch_callback {
             my $args_hash = shift;
             # {
             #  filename => 'cb//somefilename',
             #  cd => 'AVERAGE',
             #  start => 1401295291,
             #  end => 1401295591,
             #  step => 300 }

             # do some clever thing to get that data ready

             return {
                 start => $unix_timestamp,
                 step => $step_width,
                 data => {
                     dsName1 => [ value1, value2, ... ],
                     dsName2 => [ value1, value2, ... ],
                     dsName3 => [ value1, value2, ... ],
                 }
            };
         }

NOTE

       If you are manipulating the TZ variable you should also call the POSIX function tzset(3)
       to initialize all internal state of the library for properly operating in the timezone of
       your choice.

        use POSIX qw(tzset);
        $ENV{TZ} = 'CET';
        POSIX::tzset();

AUTHOR

       Tobias Oetiker <tobi@oetiker.ch>